1. Field of the Invention
The present invention relates to methods and apparatus for forming optical fiber and more particularly, to methods and apparatus for forming optical fiber having improved characteristics.
2. Technical Background
Attenuation and sensitivity to heat (or thermal) aging may be critical attributes of optical fibers, particularly for high data rate optical fibers. In making optical fibers, it may be necessary or desirable to minimize attenuation loss in the intended window of operation for the fiber. Attenuation in an optical fiber can increase after fabrication of the fiber because of a phenomenon called “heat aging.” Heat aging is the tendency of some optical fibers to increase in attenuation over time following formation of the fibers due to temperature fluctuations in the fiber's environment. Typically, the attenuation change from heat aging may be apparent at approximately 1200 nanometers (nm) with increasing effect up to about 1700 nm in a spectral attenuation plot. Furthermore, attenuation may be the result of Rayleigh scattering loss. Therefore, improved methods that reduce fiber attenuation due to effects such as heat aging and Rayleigh scattering are desired.
One method for manufacturing fibers that have reduced attenuation due to effects such as heat aging and Rayleigh scattering involves cooling fiber at a controlled rate while drawing fiber from a draw furnace apparatus. However, cooling fiber at a controlled rate can be difficult to achieve in conventional processes for manufacturing optical fibers. Such processes generally involve the vertical downward draw of fiber along a linear pathway along which there is typically little space available for adding additional equipment, such as equipment for cooling fiber at a controlled rate, without adding height to the overall system. Because adding height to an existing system can add significant cost to the system, processing systems in which space is available for controlled cooling without necessitating an increase in overall system height are desired.